The LSUHSC New Orleans
Emergency Medicine Interest Group
The Student Procedure Manual
Radial Artery Puncture for Arterial Blood
- Arterial blood gas sampling to confirm/rule-out hypoxia, CO2 retention, acid-base
abnormality, CO poisoning (COHb), nitrate poisoning (MetHb) and to obtain arterial
blood for other blood tests such as ammonia level, lactic acid level and etc...
- Severe atherosclerosis
- Infection/bum/previous surgery or cutdown at site
- Decreased collateral flow
Allen test: The radial artery is the most common site for ABG sampling. One
of the risks of this procedure is thrombosis, which would decrease or block
perfusion distally. It is an absolute necessity to ensure that the ulnar artery
provides good collateral blood flow to the hand. The Allen test verifies the
presence of a patent ulnar artery providing sufficient blood flow to keep the
hand perfused in the event of loss of flow from the radial artery.
- Have the patient make a tight fist.
- Using your thumbs, occlude both the radial and ulnar arteries just proximal
to the flexor crease of the wrist.
- Ask the patient to open his or her hand.
- After a few seconds of occlusion, the hand should be pale.
- Release pressure on the ulnar artery, while keeping the radial artery occluded.
- Color should return to the hand within 6 seconds. (the hand should flush red)
- Repeat the test, but release the pressure on the radial artery only.
- The time for color to return to the hand should be about the same.
- If it takes significantly longer for color to return to the hand when the ulnar
artery is released, as compared to the radial artery, collateral circulation
to the hand is insufficient and another site for ABG sampling should be chosen.
- If color returns quickly after the ulnar artery is released, proceed with the
Equipment (usually provided in an ABG sampling kit)
- 3-5 ml pre-heparinized syringe (if syringe is not preheparinized, draw 1 ml
of heparin solution (1: 1000 or 1000 IU per ml) into the syringe, moving the
plunger up and down a few times to coat the barrel of the syringe. Then expel
all of the visible heparin through the needle immediately before drawing blood,
leaving only a trace of heparin in the needle and in the syringe.)
- 25 gauge needle
- Alcohol swabs
- Iodine-based antiseptic swabs
- Gauze pad
- Cup or bag of ice
- Protective equipment for universal precautions
- Wear latex gloves
- The patient's hand should be supinated and the wrist dorsiflexed slightly, with
the forearm resting on a comfortable surface. No tourniquet is used.
- Do an Allen test.
- Palpate the radial artery pulse about 2 cm proximal to the flexor crease of
- Prepare the area with an iodine-based antiseptic swab and/or an alcohol swab.
- With your non-dominant hand, use the index and middle fingers to locate and
trap the radial artery, maintaining control of it in a lcm (approx.) space between
the fingers along the artery.
- Holding the syringe like a pencil with the needle bevel up, enter the skin with
the needle angled towards the flow of blood, in the space between the fingers
controlling the artery.
- Upon entering the lumen of the artery, blood should flow into the syringe, pushing
the plunger back due to the arterial pressure. Allowing the syringe to passively
fill in this manner ensures that a venous sample is not being taken. A very
slight pull on the plunger may be necessary. If no blood flows into the syringe,
withdraw slightly because the needle may have passed through both walls of the
vessel. It may be possible to see the blood pulsate into the syringe as it fills,
further evidence that the sample is arterial in origin.
- If no blood flows into the syringe, it may be necessary to slowly withdraw partially
and redirect the syringe, using the palpable pulsation under the fingers as
a guide. In this case, do not withdraw completely out of the skin, merely pull
back and redirect towards the pulsation.
- After 2-3 i-nl of blood has been obtained, withdraw the needle quickly and apply
the gauze pad using firm pressure at the site for at least 5 minutes. If the
patient has a coagulopathy, 10-15 minutes of firm pressure is required. The
goal is to avoid a large hematoma or a possible compartment syndrome. One trick
is to use one's elbow to maintain pressure on the gauze pad, leaving the hands
free. If the patient is reliable, he/she can be instructed to keep pressure
on the pad, or an assistant can hold it.
- Remove any air bubbles from the sample by first removing and disposing of the
needle, then hold the syringe upright and tap the syringe to cause any bubbles
to rise. Cover the tip of the syringe with a gauze pad to catch any expelled
blood. Gently push the plunger to expel all the air bubbles. The gauze catches
any expelled blood. Cap the syringe so that it is airtight, and roll it between
the hands to mix the contents. Place the capped syringe on ice.
- Note the time of day, patient's current temperature, and the inspired oxygen
concentration on the lab slip and make sure the sample gets to the lab quickly.
- Thrombosis, hematoma, arterial embolism, arterial spasm, arterial insufficiency
with tissue loss, infection, hemorrhage, pseudoaneurysm formation and compartment
Interpretation of Results (just the very basics)
- pH: 7.35-7.45
- pO2: 80-100 mmHg
- pCO2: 35-45 mmHg
- SaO2: >95%
- [HCO3-]: 22-28 mmol/L
- Base difference (excess/deficit): -3 to +3 mmol/L
- Make sure that at least 5 minutes of firm pressure is kept over the arterial
puncture site to prevent hematoma.
Related tests / procedures
- Use pulse oximetry instead of repeated arterial blood gas samples if the
only thing being evaluated is oxygenation. Order a standard blood chemistry
panel to calculate the anion gap in metabolic acidosis:
- Anion gap = [Na+] - ([CI-] + [HCO3-]
- Normal range = 8-12 mmol/L
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